1. Field of the Invention
The present invention relates generally to machine tools, and more specifically to a machining unit for a program-controlled milling and drilling machine.
2. Discussion of Related Art
Machining units having swivel and/or rotary heads for selectively machining a workpiece horizontally or vertically at one position, have been used for some time. Such units typically carry a working spindle and provide movement of the spindle in horizontal and vertical axes.
German patent publication 44 02 084 describes a machining unit having a support housing movable along a machine column. In this unit, the end wall is slanting with respect to vertical by 45° and is downwardly inclined. The end wall guides a swivel milling head having a mounting surface also inclined by 45° relative to the vertical. The swivel milling head carries a working spindle arranged at 45° relative to the axis of rotation which, by corresponding rotation of the swivel milling head, can be pivoted between horizontal and vertical machining positions. The support housing for the swivel head accommodates a controllable motor having a shaft coaxial with the axis of rotation. The shaft drives the working spindle via a pair of bevel gears and a set of sliding gears at two different speeds, as desired.
One shaft of the spindle motor is hollow and surrounds a solid shaft passing through the motor housing and the swivel head with enough clearance for turning the swivel head. A worm drive is attached to the inner end of the hollow shaft. The housing of the swivel head is mounted on the outer lower end of the shaft. An annular swivel head end projection, coaxial with the 45° axis of rotation, includes radial serrations. An annular recess of the head support accommodates complementary radial serrations. The swivel head is positively fixed at a specified angular position by positive engagement of both radial serrations. The central solid shaft is axially slidable and connected with a resiliently biased pressure medium cylinder via an end plate.
In this known device, the fixation of the swivel head at given angular positions means that machining of a workpiece is only possible at given spindle positions. In addition, the manner of fixing the swivel head is relatively complicated.